Polymorphisms in the Apolipoprotein E gene encode functional variants which differentially determine the rate at which neuronal repair can occur, and are associated with differences in expression of neurodegenerative processes, including traumatic brain injury. It is proposed that the accuracy of prediction of outcome after head injury will be significantly increased by inclusion of APOE genotype alone, or in combination with other variables such as severity of head injury, cognitive, electroencephalographic or neuroradiologic measures, or treatment strategies.